The present invention relates to an offset printing ink or offset printing varnish, comprising at least one binder and where appropriate at least one colorant.
Offset printing inks and printing varnishes are widely used for printing onto food packaging, for example for printing onto food packaging in the form of folding cartons using the sheet-fed offset process. Printing inks and printing varnishes that are permitted for this application sector must meet certain conditions so that the possibility of the packaged food being contaminated by components of the printing ink or printing varnish that are potentially hazardous to health can be ruled out. In particular, there are limit values on the maximum permissible quantity of components that are permitted to pass through from the printed outside of the packaging, that is to say towards the food. This phenomenon is called migration.
Offset printing inks include one or more colorants, typically pigments, and one or more binders that bind the colorants to the surface of the printing substrate by forming a film (in contrast, offset printing varnishes contain no colorants and are used for example to form an additional protective coat over the printing ink). The binder or binders, for their part, include one or more resin components and a solvent which dissolves the resin components in the printing ink or printing varnish and reduces the viscosity to the required level, wherein the solvent enables physical and/or chemical drying of the printing ink or printing varnish after the printing procedure in that it evaporates, is absorbed by the printing substrate or undergoes oxidative curing. Since in all cases the solvent has by far the greatest volatility of all the components of the printing ink or printing varnish, it makes a very substantial or even the only contribution to the problems of migration, with the result that, when offset printing inks and printing varnishes that are suitable for food packaging are developed, hitherto considerations have been limited to the selection of suitable solvents.
For example, DE 10 2007 012 264 A1 proposes a printing ink or printing varnish for food packaging, comprising a binder having a resin component and a solvent component, wherein the solvent or components of the solvent are a food or food additive. In this case, contact between the packaged food and the migrating solvent is harmless to health since the solvent is a component that can itself be used in foods.
Despite these developments, offset printing inks and printing varnishes may fundamentally only be used for printing onto the outside of food packaging, that is to say the printing inks and printing varnishes must in particular not come into direct contact with the food, since in this case the food may be contaminated not only by the solvent but also by all the other components of the printing ink or printing varnish, in particular with the colorant or colorants and binder or binders. However, the offset printing inks and printing varnishes known from the prior art always also contain components that are potentially hazardous to health or whereof the effects on health are unknown.